This invention relates generally to the drainage of aqueous humor from an eye to relieve the elevated pressure characteristic of glaucoma. More specifically, the present invention relates to an implantable glaucoma shunt device and related method, which prevents or limits drainage of aqueous humor from the eye initially after implant to avoid damage to the eye, and additionally allows the rate of flow of aqueous humor from the device to be initiated or adjusted periodically after implantation.
Aqueous humor is continuously produced by the ciliary body in the posterior chamber of the eye, and from there it flows through the pupil into the anterior chamber of the eye. In order to maintain relatively constant intraocular pressure, aqueous humor must be drained away continuously. It passes primarily through the trabecular meshwork of the anterior chamber and into the canal of Schlemm, before draining into the veins leaving the eye.
Normal intraocular pressure is typically about 15+/xe2x88x924 mm Hg, but may rise to 21 mm Hg. Pressures within the eye that are substantially above this range are considered abnormally high. Chronically elevated intraocular pressure (resulting, for example, from a defect in intraocular drainage) can give rise to glaucoma. Glaucoma can cause irreversible damage to certain structures of the eye, including the optic nerve, and is a leading cause of blindness in the United States.
There are many types and causes of glaucoma. Treatment of the disease depends on both the patient and the form of glaucoma. As a rule, the damage caused by glaucoma can not be reversed. The goal, therefore, of glaucoma treatment is to prevent further damage and to preserve existing vision.
Glaucoma can often be controlled with medical therapy, typically through topical medications, such as pilocarpine, timolol maleate, betaxolol, or epinephrine, and also through systemic medications, including acetazolamide. Medical therapy either decreases the rate of production of aqueous humor, or increases its outflow from the anterior chamber. However, with many patients these procedures are not effective because the patients fail to follow the treatment prescribed, due to either negligence or the relatively high cost of the medication. Other potential problems with medical treatment include side effects and inadequate control of the intraocular pressure.
If the maximum-tolerated dose of medication fails to control the intraocular pressure, then laser trabeculoplasty or filtering surgery to increase aqueous drainage is usually indicated. These procedures seek to increase the rate of outflow of aqueous humor. Other types of surgical procedures seek to reduce the formation of aqueous humor, by destroying the tissue where it is created. These procedures are typically indicated only after filtering surgery has failed. If such filtering surgery has failed to control the intraocular pressure, or if the patient has a poor prognosis for filtering surgery, implantation of a glaucoma shunt may be indicated.
Glaucoma shunts typically drain aqueous humor from the anterior chamber of the eye to the fibrous capsule (bleb) which forms around a collecting device placed on the posterior portion of the globe of the eye, and the humor is then reabsorbed into the vascular system. The bleb is formed apparently due to an immune response against the shunt, which the host recognizes as a foreign body. Bleb formation is essential for a successful implant procedure and recovery by the patient.
Glaucoma shunts typically consist of a silicone elastomer catheter which is inserted into the anterior chamber, and which connects to an episcleral plate or an encircling band. Episcleral plates are commonly made of silicone elastomer, polypropylene or acrylic materials.
Glaucoma shunt implantation is subject to a number of complications. In the early post-implantation period, excessive drainage of aqueous humor from the anterior chamber can cause low intraocular pressure (hypotony), resulting in shallow anterior chamber depth. This can lead to choroidal detachment, hemorrhage or hypotony maculopathy. The hypotony is typically alleviated as the fibrous capsule forms around the posterior plate or encircling band. In the long-term, excess fibrous tissue can obstruct the flow of aqueous humor from the shunt through the bleb and into the vascular system. This causes an increase in the intraocular pressure and results in clinical failure of the device. The shunts known in the art typically have had some ligature or plug which was removable or biodegradable, to prevent flow of aqueous humor through the device for an initial period after implantation, allowing sufficient time for the bleb to form before drainage begins. Further, if the flow rate from the shunt is too low, insufficient amounts of aqueous humor may be drained from the eye. Such drainage may be insufficient to lower intraocular pressure to a degree which will prevent further damage from glaucoma.
Prior art shunt devices had attempted to adjust the flow rate of aqueous humor from the device by varying the radius of the shunt tube. However, the rate of flow (f) of aqueous humor through a tube is proportional to the radius (r) of the shunt tube to the fourth power (f xe2x88x9d r4). Therefore, attempts to a adjust the flow rate by changing the radius of the shunt tube were not practical due to the inability to make precise adjustments. For example, changing the radius of the shunt tube from 2 mm to 3 mm resulted in an increase of flow rate from 16 to 81. Therefore, a shunt device that allows the flow rate of aqueous humor to be adjusted in a linear fashion, which would allow precise and accurate adjustments to be made in the flow rate of aqueous humor, would be desirable.
In order to adequately relieve intraocular pressure, it is advantageous for an implant device to meet three requirements: (1) the device must be able to block most or all of the flow of aqueous humor through the device for the initial period after implantation until the bleb has formed about the device; (2) the device must be able to prevent collapse of the eye after the flow of aqueous humor through the device is increased to a level sufficient to relieve intraocular pressure; and (3) the device must allow aqueous humor to drain from the eye at a sufficient rate to successfully treat the glaucomatous condition. Prior art shunt devices to prevent excess flow of aqueous humor from the device utilized complicated systems of pressure sensitive slit valves, check valves or photosensitive polymers.
Accordingly, there has been a need for a novel glaucoma shunt which, in the immediate post-implantation period, can provide resistance to flow to prevent hypotony and its complications until the fibrous capsule forms around the end of the shunt from which the aqueous humor drains, to prevent damage to the eye. Additionally, such a shunt should be capable of having its flow rate initiated or increased, and thereafter adjusted incrementally in a quick and easy fashion, after implantation by the physician. Further a glaucoma shunt is needed which accomplishes its desired function and is easy to manufacture and use, and which provides a desirable shunting function reliably over an extended period of time. The present invention fulfills these needs and provides other related advantages.
The present invention resides in an improved glaucoma drainage device and in a method of using the device for shunting excess aqueous humor from the eye. The device and methods of the invention allow for periodic post-implantation linear adjustment of the flow rate of aqueous humor from the anterior portion of the eye through the device to the outside of the eye.
More specifically, the glaucoma drainage device comprises a hollow tubular member having first and second ends, with the first end being sealed and the second end being open and joined to the first end by a wall, and comprising a material which may preferably be perforated by a low power laser after implantation of the device. The glaucoma drainage device may further comprise a plate attached to the second end. This plate would allow easier attachment of the device to the eye during implantation and also facilitate in the adequate formation of a bleb while preventing excessive fibrosis around the second end.
Further, the wall of the tubular member may contain preformed depressions over various segments along the wall""s length which may exist as scalloped sections or grooves along the length of the wall, wherein the wall at these segments is thinner than at the remaining segments of the wall. These depressions are located in the portion of the wall of the tubular member situated in the anterior portion of the eye after implantation, allowing perforation of the tube at these points with less laser energy (e.g., from a lower powered laser) than would be required for the remaining thicker segments of the wall. By perforating the tubular member rather than varying the radius of the tubular member, the flow rate of aqueous humor through the device can be modified in a precise, regulated linear fashion.
Additionally, the wall of the tubular member may have one or more openings prior to implantation, to allow aqueous humor to drain through and from the device immediately after implantation, at a flow rate low enough to prevent the dangers resulting from a rapid post-implantation decrease in intraocular pressure, but inadequate to lower intraocular pressure sufficiently to prevent damage associated with glaucoma. These initial openings are located within the portion of the tubular member residing in the anterior portion of the eye after implantation. This initial flow rate can then be increased to allow adequate flow of aqueous humor from the device to treat the glaucomatous eye (i.e., prevent damage associated with glaucoma and associated excess pressure), by the creation of one or more openings or perforations (holes) within the portion of the wall of the tubular member located within the anterior chamber of the eye after implantation as previously described. The flow rate can be adjusted in a linear fashion periodically as required by the attending physician, in order to increase the flow rate of aqueous humor in a precise manner and thereby lower intraocular pressure, by the simple method of placing additional perforations within wall of the tubular member. The perforations or openings in the wall of the tubular member are preferably and conveniently made using a laser.
In an alternative embodiment of the invention, the glaucoma drainage device comprises a hollow tubular member, having a first end and a second end, wherein the second end is ensconced in a sealed reservoir. The first end of the tubular member is inserted into the anterior chamber of the eye, and the reservoir in which the second end is ensconced may be located outside the eye on top of the sclera. The flow rate of aqueous humor through the device may be initiated and thereafter periodically adjusted in a linear manner at any time after implantation in order to increase the flow rate of aqueous humor and thereby lower intraocular pressure, by placing one or more openings or perforations in the reservoir. If the reservoir is located outside of the eye, the openings or perforations may be created by non-mechanical means such as a laser. Additionally, one or more openings or perforations may be placed in the reservoir prior to implantation, allowing a small rate of flow of aqueous humor from the device, but at a low level which is insufficient to relieve all of the intraocular pressure due to glaucoma.
It is also an object of the invention to provide a method for treating glaucoma comprising the insertion of an adjustable flow rate drainage device of the invention into the anterior chamber of the eye to allow linear adjustment of intraocular pressure.
More specifically, the method for treating glaucoma with an implanted shunt of the invention includes the steps of inserting the first sealed end of the tubular member into the anterior chamber of the eye, and securing the second open end of the tubular member to the sclera of the eye. The second open end may have a plate secured to it; the plate thereby being fastened to the sclera of the eye. Initial post-implantation flow of aqueous humor through the device may be prohibited, or alternatively, may be allowed at a minimal rate until the point in time that an increased flow rate could be safely initiated without endangering the patient. This initial flow rate would take place from one or more openings or perforations within the portion of the wall of the tubular member located within the anterior chamber of the eye and would allow a small amount of drainage of aqueous humor, at a rate that would not be dangerous to the eye, but would not be sufficient to alleviate the intraocular pressure due to glaucoma within the eye. A sufficient post-implantation period of time is allowed to pass and the physician may thereafter place small openings or perforations in the portion of the portion of the wall of the tubular member located within the anterior chamber, whereby the flow of aqueous humor from the anterior chamber of the eye into the tubular member and flow out of the tubular member is initiated or increased linearly to a rate sufficient to treat the glaucomatous eye, depending on whether the device was initially sealed, and the excess aqueous humor will be reabsorbed into the vascular system. The initial opening(s) in the wall of the tubular member could be made prior to implantation, or may be created after implantation. The glaucomatous condition can thereafter be monitored by the physician, and if intraocular pressure increases, additional openings or perforations may be placed within the portion of the wall of the tubular member located within the anterior chamber of the eye to increase the flow rate of aqueous humor from the eye, through the device. Additional perforations may be created in this portion of the wall of the tubular member at any time after implantation to increase the flow of aqueous humor. These perforations may be made by a laser, which is directed through the cornea of the eye to the tubular member. A low watt laser is used so as to avoid damage to the eye. This procedure of creating additional perforations to adjust the flow rate of aqueous humor from the device may be done on an out-patient basis.
Accordingly, it is an object of the present invention to provide a device or apparatus for implant in or at the eye, and a method to treat glaucoma by reducing intraocular pressure in the anterior chamber in stages, by allowing little or no aqueous humor to drain from the eye through the implant during the initial post-implantation period, and thereafter allowing the flow rate of aqueous humor through the device to be adjusted in a linear fashion easily, quickly, precisely and relatively painlessly at various post-implant time periods, as required.